Sharif Digital Repository

NiTi alloys have exhibited significant potential as a matrix of wear resistant composites. In this study, in order to examine the effect of starting materials on the wear performance of NiTi-based composites, both elemental Ni/Ti and prealloyed NiTi powders were used to fabricate NiTi-6wt% nano-Al2O3 composites using hot isostatic pressing (HIP). Nanoindentation and microhardness test results indicate that the composite samples produced from the elemental Ni/Ti powders exhibited higher hardness and lower pseudoelasticity properties than those of the samples fabricated from the prealloyed NiTi powders; this is attributed to the higher amount of... 

In contrast to Western countries, traditional floor-seating cultures are prevalent in Korea, Japan, the Middle East, and Africa, where sitting on the floor in static positions such as squatting, kneeling, or sitting cross-legged is common. Most studies on sitting posture have predominantly focused on chair sitting in Western cultures, resulting in a cultural bias. This study aimed to investigate the effects of different cushion types (floor and traditional cushions of 3-cm, 5-cm, and 8-cm thickness) and seating postures (cross-legged, mother's leg, and kneeling) on measures of postural stability, trunk muscle activity, rotational spinal stability, and subjective postural stability in an... 

Gelatin methacrylate (GelMA) was proved to be a promising bioink for corneal stromal cell delivery. However, GelMA has low mechanical properties which makes it difficult to be suturable and handled for clinical applicattion. In this study, three different ratios of 12.5 % GelMA and 10 % PEGDA were investigated for corneal stromal cells delivery. The mixture containing 75 % GelMA and 25 % PEGDA (75G25P) was found to have reasonable cell viability and suturing strength. Moreover, collagen nanofibers were incorporated into 75G25P hydrogel to improve the mechanical and biomimetic properties of the construct (75G25P-E). A hybrid structure was obtained by injecting the optimized bioink on the... 

Equal channel angular pressing is an outstanding method for imposing large plastic deformation to metallic materials without any decreasing in cross section area of as processed samples. In this paper, the effect of working temperature, ram speed and the number of passes on the formation of adiabatic shear bands in Al6061 during equal channel angular pressing was investigated. Billets of the alloy were processed up to four passes via route BC from room temperature to 200°C with two ram speeds using a die that imparts an effective strain of ∼1.1 per pass. The results have demonstrated that the onset of the adiabatic shear banding in this alloy strongly depends on the ram speed: more... 

Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or... 

Abstract: 3D bioprinting technology is a promising approach for corneal stromal tissue regeneration. In this study, gelatin methacrylate (GelMA) mixed with corneal stromal cells was used as a bioink. The visible light-based stereolithography (SLA) 3D bioprinting method was utilized to print the anatomically similar dome-shaped structure of the human corneal stroma. Two different concentrations of GelMA macromer (7.5 and 12.5%) were tested for corneal stroma bioprinting. Due to high macromer concentrations, 12.5% GelMA was stiffer than 7.5% GelMA, which made it easier to handle. In terms of water content and optical transmittance of the bioprinted scaffolds, we observed that scaffold with... 

We studied the flow stress and microstructural changes of nanostructured Al-6063 alloy produced by mechanical alloying at various temperatures and strain rates. The analysis of flow curves was performed by a constitutive equation, and the stress exponent and activation energy were determined as functions of strain. The deformation mechanisms were elaborated through microstructural observations by electron backscattering diffraction and transmission electron microscopy. Coarsening of the subgrains and grain growth upon deformation was monitored and related to the Zener–Hollomon parameter  

Ultrafine-grained (UFG) Al6063 alloy reinforced with 0.8 vol% nanometric alumina particles (25 nm) was prepared by reactive mechanical alloying and direct powder extrusion. Transmission electron microscopy and electron backscatter diffraction analysis showed that the grain structure of the nanocomposite composed of nanosize grains (<0.1 μm), ultrafine grains (0.1–1 μm) and micronsize grains (>1 μm) with random orientations. Mechanical properties of the material were examined at room and high temperatures by compression test. It was found that the yield strength of the UFG composite material is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation... 

Nanostructured AA6063 (NS-Al) powder with an average grain size of ∼100 nm was synthesized by high-energy attrition milling of gas-atomized AA6063 powder followed by hot extrusion. The microstructural features of the consolidated specimen were studied by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques and compared with those of coarse-grained AA6063 (CG-Al) produced by hot powder extrusion of gas-atomized powder (without using mechanical milling). The consolidated NS-Al alloy consisted of elongated ultrafine grains (aspect ratio of ∼2.9) and equiaxed nanostructured grains. A high fraction (∼78%) of high-angle grain boundaries with average... 

The microstructure and phase transformational behavior of NiTi-based composites reinforced with 6 wt.% of α-alumina nanoparticles have been investigated. Two kinds of starting materials, elemental Ni–Ti and prealloyed austenitic NiTi, were used to prepare the composites. The samples were consolidated using a hot isostatic pressing method. The X-ray diffraction results showed that while unreinforced NiTi mainly contained B2 phase at room temperature, martensitic B19′ phase appeared in the microstructure after addition of the α-alumina nanoparticles. The differential scanning calorimetry measurements indicated that the martensitic transformation temperatures were elevated in the composite... 

An experiment was conducted to determine whether allowing an aluminum melt to solidify in the crucible and later remelting it would improve the quality of the melt and the casting. To investigate this, data were collected through reduced pressure test, density measurement, metallography, X-ray radiography and tensile testing and analyzed statistically. Results indicated that remelting improved the quality of the melt by reduction of the number of defects in the casting and their area and volume fractions. The improvement in elongation of remelted specimens was found to be statistically significant. Analysis of deformation characteristics showed that the improvement in elongation is due to... 

Spin-Transfer Torque RAM (STT-RAM) is a promising alternative to SRAM for implementing on-chip L2 and L3 caches. One of the most critical challenges in STT-RAM is reliability due to limited write endurance, which results in insufficient lifetime, as well as various types of errors. Previous studies have focused on either presenting various cache architectures/management techniques to improve the lifetime of STT-RAM caches or utilizing different Error Correcting Codes (ECCs) to protect against the permanent and transient errors. However, there is no quantitative analysis in the literature to determine the impact of ECCs on the lifetime of the STT-RAM caches. This paper formulates this impact... 

In current studies, equal channel angular pressing process (ECAP) and modified ECAP processes are simulated under ideal conditions to compare the deformation characteristics. The deformation behaviour is more complicated and the strain induced during the processes is highly non-uniform in the modified ECAP processes except in the equal channel multi-angular pressing (ECMAP) process with Route C. The strain homogeneity is more of a possibility with ECAP and ECMAP with Route C processes. The deformation stress state is widely distributed in nature in modified ECAP processes than in conventional ECAP. In addition, the load requirements are also higher in modified ECAP processes with that of the... 

Microsatellite instability (MSI) refers to alterations in the length of simple repetitive genomic sequences. MSI status serves as a prognostic and predictive factor in colorectal cancer. The MSI-high status is a good prognostic factor in stage II/III cancer, and predicts a lack of benefit to adjuvant fluorouracil chemotherapy in stage II cancer but a good response to immunotherapy in stage IV cancer. Therefore, determining MSI status in patients with colorectal cancer is important for identifying the appropriate treatment protocol. In the Pathology Artificial Intelligence Platform (PAIP) 2020 challenge, artificial intelligence researchers were invited to predict MSI status based on... 

Cu-CNT composites were fabricated by a flake powder metallurgy method, and their microhardness, electrical conductivity, frictional and wear properties were investigated. Homogenous distribution of CNTs in fine-grained Cu matrix was obtained using this process. Microhardness increased with the addition of CNT vol% up to 8% to the Cu matrix, while the conductivity decreased to 79.2 IACS %. Results showed that CNTs play a major role in improving wear resistance by forming a CNT-rich film that acts as a solid lubricant layer. In the synthesized composites, Cu- 4 vol% CNT composite exhibited the best wear and friction properties. The dominant wear mechanisms for the Cu-CNT composites were... 

Ultrafine-grained (UFG) Al6063 alloy reinforced with 0.8 vol% nanometric alumina particles (25 nm) was prepared by reactive mechanical alloying and direct powder extrusion. Transmission electron microscopy and electron backscatter diffraction analysis showed that the grain structure of the nanocomposite composed of nanosize grains (<0.1 μm), ultrafine grains (0.1-1 μm) and micronsize grains (>1 μm) with random orientations. Mechanical properties of the material were examined at room and high temperatures by compression test. It was found that the yield strength of the UFG composite material is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation... 

The microstructure and mechanical properties of the ultra-fine grained (UFG) Al6063 alloy reinforced with nanometric aluminum oxide nanoparticles (25 nm) were investigated and compared with the coarse-grained (CG) Al6063 alloy (∼2 μm). The UFG materials were prepared by mechanical alloying (MA) under high-purity Ar and Ar-5 vol pct O2 atmospheres followed by hot powder extrusion (HPE). The CG alloy was produced by HPE of the gas-atomized Al6063 powder without applying MA. Electron backscatter diffraction under scanning electron microscopy together with transmission electron microscopy studies revealed that the microstructure of the milled powders after HPE consisted of ultra-fine grains... 

We studied the flow stress and microstructural changes of nanostructured Al-6063 alloy produced by mechanical alloying at various temperatures and strain rates. The analysis of flow curves was performed by a constitutive equation, and the stress exponent and activation energy were determined as functions of strain. The deformation mechanisms were elaborated through microstructural observations by electron backscattering diffraction and transmission electron microscopy. Coarsening of the subgrains and grain growth upon deformation was monitored and related to the Zener-Hollomon parameter  

Hot deformation behavior of Al6063 alloy produced by direct powder extrusion was studied by means of uniaxial compression test in the temperature range between 300 and 450°C and strain rate range between 0.01 and 1s -1. Electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM) were utilized to study the microstructure of the material before and after the hot deformation. The microstructure of the extruded alloy consisted of elongated grains within a subgrain structure and small grains free of low angle grain boundaries (LAGBs). An equiaxed duplex microstructure consisting of large substructured grains and fine grains separated by high angle grain boundaries... 

A modified plastic yield function is proposed to predict the consolidation behavior of nanostructured metal powders and metal-matrix nanocomposite powders under uniaxial compaction. The validity of the model is verified for nanocrystalline Al6063 (~100nm) alloy reinforced without and with 0.8vol.% Al2O3 nanoparticles (~25nm). The plastic deformation propensity of these powders is analyzed by linear compaction equations. The yield stress of the powder compacts is shown to be influenced by the nano-scale grains and the reinforcement nanoparticles